HyperCODA - Simulation and Validation of a Hypersonic Reentry Vehicle along its Trajectory

Kurzfassung

Designing a hypersonic reentry vehicle presents significant challenges. Particularly important is the prediction of thermal loads, a critical factor in vehicle performance and structural integrity. While atmospheric testing is often prohibitively expensive (requiring deployment in the upper atmosphere) and wind tunnels cannot fully replicate the flow conditions of the entire trajectory, computational simulations emerge as a compelling alternative. However, simulating hypersonic reentry introduces its own complexities. This is due to the extreme and interdependent physical phenomena encountered during reentry. These include strong shocks, non-equilibrium gas dynamics in upper-atmospheric conditions and numerically stiff chemical reactions induced by rapid compression and heating.

The goal of this work is to validate HyperCODA across the flight envelope of reentry vehicles. HyperCODA is an extension of the modular flow solver "CFD by ONERA, DLR and Airbus" (CODA), including non-ideal gas thermodynamics, gas mixtures, and chemical reactions. To validate and demonstrate HyperCODA's capabilities for complex, industrially relevant applications, a comparison is made between the simulation results of HyperCODA and those of TAU-RF, DLR's well-established and widely employed CFD solver for spaceflight applications. Multiple points along the atmospheric reentry trajectory of a waverider geometry, as shown in Figure~\ref{fig:flowfield}, are simulated. For these, the results of HyperCODA and TAU-RF are compared. Both HyperCODA and TAU-RF utilize Reynolds-Averaged Navier-Stokes (RANS) equations with the Spalart-Allmaras turbulence model in its negative formulation. This approach enables reasonably high fidelity computations, while keeping the computational cost relatively low. Initial simulations are compared: A trajectory point in the lower atmosphere is chosen, such that the denser atmosphere and lower surface temperatures allow for a non-reactive ideal gas approach. The TAU-RF result depicts the density distribution for the time-dependent temperature evolution of the waverider within a coupled multi-physics simulation, where the waverider heats up during the reentry. As HyperCODA is not yet integrated into the toolchain, the HyperCODA simulation was performed using adiabatic walls, leading to differences in the density distribution. While the main flow features, such as shock position or the location of the air cushion remain similar, the regions of higher density are more extensive both above and below the waverider, when compared to the TAU-RF results. Future work will incorporate HyperCODA into the toolchain and extend the analysis to more complex flight regimes at higher altitudes, using HyperCODA's reactive and non-equilibrium models.